Field of the Invention
1. The present invention generally relates to vehicle lighting systems of the type which utilize a high brightness light source, such as an arc lamp, coupled to fiber optic light conductors in order to provide forward illumination in aerodynamically styled vehicles. More specifically, this invention relates to an improvement in such lighting systems in which a moveable mask is used to generate multiple beam patterns with a set of fiber optic light conductors coupled to a single light source.
2. Description of the Prior Art
Conventional headlamp systems have met the need to produce upper and lower headlamp beam patterns with two or more light sources, either arc discharge or filaments. Single-headlamp systems (one headlamp on each side of the vehicle) must make compromises relating to performance. Performance trade-offs must be made to provide high and low beam patterns with a single optical system. Differing functions and light distributions of the two patterns make the problem of providing upper and lower beams more complicated than adjusting the aim of a single beam. Two-headlamp systems (two headlamps for each side of the vehicle) provide two optical systems and improve performance in terms of the high and low beam patterns generated, but at the expense of adding headlamps.
U.S. Pat. No. 4,811,172, referenced above, discloses a "line-of-light" lighting system that provides an improved method of producing beam patterns as compared with what can be achieved with conventional headlamp optics. In one embodiment of the "line-of-light" headlamp as disclosed in that patent, the lighting system includes two high intensity light sources which are respectively coupled to first and second pluralities of fiber optic light bundles. Both pluralities of fiber optic light bundles are positioned relative to lens members mounted across the vehicle in a pattern conforming to the shape of the vehicle body. The light from the first high intensity light source provides the low beam forward illumination of the vehicle, and the light from the second high intensity light source provides the high beam forward illumination of the vehicle.
U.S. Pat. No. 4,868,718 discloses an improvement on the system disclosed in U.S. Pat. No. 4,811,172 wherein only one high intensity light source is used while still providing both the low beam and high beam forward illumination of the vehicle. A moveable optical member is arranged between a set of lens elements mounted across a vehicle and the fiber optic light bundles. This moveable optical member comprises a plurality of prisms in an integral bar structure which may be moved from side-to-side or up-and-down. The movement of this "prism-bar" alters the apparent optical position of the fiber optic light bundles relative to the lens elements in such a manner as to provide all of the forward illumination needs of the vehicle from the single light source including high and low beam patterns. The "prism-bar" is advantageous in that it requires only a single light source. However, it requires precise manufacture and alignment, increasing both the cost and fragility of the unit.